Adsorption; heavy metals; coal; carbon

Immobilization ability of natural coals and activated carbons to remove heavy metals from aqueous solutions is reported and discussed. To characterize texture of the studied samples, internal surface area, surface hydrophilicity, carbon aromaticity and zeta potential in aqueous dispersion were measured. As heavy metals, lead (II), copper (II) and cadmium (II) cations were investigated. Adsorption behaviour of the cations was studied using both adsorption isotherms at equilibrium and kinetics of the adsorption process. In addition, flow calorimetric measurements were applied to determine the adsorption enthalpy. Influences of pH and temperature were investigated as variables affecting adsorption behaviour of the cations on coals. Different models to describe the adsorption process were examined. Based on the investigations performed, thermodynamic calculations as well as considerations on immobilization mechanisms of the metalic ions on coal surface are presented.